Ammonium nitrate gas-generating composition



AM" M '()N 1U M NITRA TE coMPosrrIoN States atgt Jack Linsk, Highland, ind, assignor to Standard on can puny, Chicago,- Ill a co'rporationof Indiana No FiledJu'ne 21 1955, Ser; No. $17,077 6 claims; or,- sa as This invention teams a composition for the generation of a gas; and pertains, more particularly, to an improved gas-generating composition comprising ammonium nitrate as the primary gas-producing component or the composition, intimately mixed with a combustible b nder material consisting essentially of plasticizedpoly vinyl acetate. Such composition is useful for the propulsion of rockets for ground-to-gro'und missiles, ship.-

to-shore missiles, air-to-ground missiles and air-to-air missiles and the compositions may also be used as propulsion means in assist take-o of military'and commercial aircraft.

Ammonium nitrate is widely used as a component of high explosives, particularly the so-called safe ex losive Even-though ammonium nitrate is classified as a high explosive, it is extremely insensitive to ordinary heating and to shock and cannot readily be detonated by the local "application of heat or by a blasting cap. Further, when ignited, ammonium nitrate alone does not burn uniformly and has a tendency to go out. In order to improve the burning quality, to utilize the excess free oxygen available-from the decomposition of the ammonium nitrate, and to provide shaped grains suitable for use in rocket motors and assist take-off motors, combustible binder material is used in the ammonium nitrate composition. The use of ammonium nitrate base compositions as solid propellants for rockets and assist takeoff units is attractive because of the cheapn'ess and availability of ammonium nitrate, because of the relatively low flame temperature of decomposition of ammonium nitrate, that is, between about 3150 and 2900 F. and because of the availability of the excess freeoxygen. The physical characteristics of ammonium nitrate and grain material pro- 'cluced therefrom introduce problems with respect to choice of binder ecomponents.- Thus solid ammonium nitrate-exists in difierent crystalline forms at difierent temperatures, the transition from one form to a different form involving a volume change of the ammonium nitrate. "and also'at about 0 F. involve 3.5% and about 3% "increase, respectively. It'would therefore appear that an -ammonium nitrate-base composition could be seriously affected by storage under the variable temperatures encountered in many parts of the world.

" One requirementfor a solid propellant grain suitable for military use is that it be ballistically stable after prolonge'd storage at temperatures as high as 170 F. or as lowas 75 F. Another requirement is that the grain not shatter, crack or malperform ballistically after being -subjected to temperature extremes; that is, 175' F. followed immediately by transfer to a cold box held at .-75 F. in a series of at least two repeated cycles. Another severe requirement imposed on solid propellant "grains is ignition at temperatures down to 75 F.- with the same igniter charge which is suitable at ambient temeratnre's. Grains must'also be able to withstand shat- 'tering at low -temperatures and distortion at high tem- -peratures'when subjected to shock. i

An obiecu orthis invention is the preparation at a gas- Volume changes which occur at about 90 F. 4

of this invention is substantially as follows;

generating composition using ammonium nitrate as the principal gas-generating-material; Another object of the invention is the preparation of a shaped propellant COme position (grain), consisting essentially of ammonium nitrate, a binder material consisting essentially of polyvinyl acetate plasticized with a plasticizer comprising at least one" nitro aromatic compound, and a combustion catalyst, which grain is dimensionally stable and nonfissuring in the temperature range between about 175 F. and F.-, Still another object is to produce a gasgeneratin'g composition comprising ammonium nitrate, a binder material consisting essentially of plasticized polyvinyl acetate, and an inorganic combustion catalyst, which gas-generating composition is suitable for use in rockets and assist take-oft units. Yet another object is the preparation of a composition which is suitable for use as a binder for a mixture of ammonium nitrate and a combustion catalyst. A further object is to provide an improved grain which is useful as a rocket fuel and as fuel for a jet assisted take-off unit. This grain is characterized by having a burning rate at 1000 p.s.i., of at least 0.10 inch per second and which is preferably of the order of 0.10 to 0.20 inch per second or more, and a pressure exponent preferably below about 0.7. Other objects will be apparent as the detailed description of the invention proceeds.

The composition of theinvention comprises ammonium nitrate, a combustion catalyst, and the binder material. The composition containson a weight basi from about 70% to about of finelyground ammonium nitrate, from about to about of a combustion catalyst, from aboutv 0.2 to about 3% of an alkalinereacting gassing inhibitor as described hereinbelow, and from about 5% to about 25% of combustible binder material. The binder contains at least, about 20% of 'a solid polyvinyl acetate resin, usually from about 20% to about 60% by weight, .the remaining components comprising at least one plasticiier material for the polyvinyl acetate, said plasticizer material containing at least one nitro aromatic compound as defined hereinbelow. Other components such as'finely divided carbon may be added to the grain composition to improve the burning rate, reduce the pressure exponent, or improve low temperature ignitability.

The polyvinyl acetate resins employed in the binder material of this invention are transparent solid vinyl acetate homopolymers of; relatively high :molec u lar weight, preferably pulverized to passthrough a #16 Standard mesh screen. The resins do not have melting points. The lowest molecular weight polyvinyl acetate resins suitable for use as base material for the binders of this invention show softening points above about C. Decomposition begins at temperatures of 200 C. to 250 C. These polymers have a specific gravity of about 1.20 at 20 1 The viscosity of the homopolymers in general lies within the rangeof from; about 50 to about 900 centipoises. For purpose of this specification and the claims based thereon, the term viscosity-is defined as viscosity in centipoises of a benzene solution containing 86 grams C. with an Ostwald viscosimeter.

The composition of the gas-producing.propellantgrain of the resin per 1000 cc. of solution determined at 20.

, asa Ammonium nitrate -.-.l. a ..s a ...te...-. 70-1090 Plastic binder a a 51025 Inorganic combustion catalyst .4 1 to5 Alkaline-reacting gassing inhibitor 0.2- to3 .0 Carbon OtoS "To the eompssition mayalso bead'ded' a surfactant in semester-005% te'2.0%-by weight tit-improve wetorties with -regard-to-cycling,f impact resistance, and hot aging, and these'will be preferred'regardless' of oxygen The term ammonium nitrate asused in this specification and inthe claims intended to means either ordinary commercialgrade-ammonium nitrate such as conventionally grainedar'nmonium nitrate containing a small amount of impurities which may be coated with a small acaag'z amount of mois ture resisting mate'rial such as petrolam turn or paraflin; or to mean military grade ammonium nitrate or mixtures of minor amounts (usually' less than 10%) of other, inorganic nitrates suchas sodium nitrate or potassium nitrate withithe ammonium nitrate. A mixture of finely ground and coarsely ground ammonium nitrate s pr f rred, and the major proportion of the ammonium nitrate is finely ground. I prefer to grind the ammonium nitrate with apart or all of the catalyst component of the composition. t

The binder of the gas-producing propellant composiacetate blendedwith a plasticizer consisting of about,

30%by weight (based on the binder) of one or" more of a group Tof nitro-substituted aromatic "compounds. This group includes dinitr'obenzene, dinitrotoluene, and certain nitro-substituted aromatic others. Examples of these others are 2,4-dinitrodiphenyl ether and the di(dinitrophenyU-polyglycol others. These are made via the 'Williamson reaction by reacting '2,4-dinitr0chl0roben ivinylacgtate ve'rysatisfactory thermoplastic binder matetion is a thermoplastic material consisting ofpolyvinyl zone with phenol or glycols as taught. in the copending application'of Wayne A; Proell and Norman J. Bowman entitled Thermoplastic Compositions filed October 27 1954, Serial No. 465,132. Other nitro ethers which may be used are dinitrophenyl propyl ether and dinitroanisole. The preferred class of nitro-substituted aromatic com- 'poundscorresponds to the general formula where R is selected from the class consisting of hydrogen, methyl, nitrophenyl, phenoxy, mononitrophenoxy and alkoxy containing 1 to 4 carbon atoms. [In the choice of plasticizer components for the ammonium nitratepreference is reserved-for highly oxygenated materialsgother factors being equal.. It is de- -si'rable to use at least one non-nitro containing plastioizer material. 4 This can be an ester of a polyhydric alcohol orpolycarboxylicacid. Examples are dialkyl phthalates, triethyl citrate, tributyl citrate, dialkyl'diglycol-ate s, di-

ethyl and dibutyl tartrate, the Flexols, e.g., triethylene glycol 'di-Z-ethyIbutyrate, also known as triglycol dih'exoate, ('Flexol 36H), triglycol dioctanoate, (Flexol 360) and polyglycol dioctanoate (Flexol 460). These commercial Flexol products are fully described 'by Buttrey in ,fPlasticizersf (1950) pages 49 and 50. The liquid plasticizer must becompatible with the polyvinyl acetate and the'nitro'a'romatic components in the ratio Oxygen balance is important and esters of higher ioxygen content are preferred when" they have no undesirable effects. Some plasticizersimpart good propg Combinations-of the, above, nitro compounds either' I --a msmfli hfihgedd t on.otioth rn asticizers produce 1a satisfactory polyvinyl acetate binders which are thermoplastic. When such binders. are mixed with ammonium nitrate, grains may be fabricated which exhibit good resistance to shock and deformation at low or high temperatures. In general, liquid plasticizers for polyvinyl acetate are used only in conjunction with one or more nitro compou dsin making binders suitable for .use in solid propellant g'rains.:;1..:;: H

Cognizance of the stoichiometric oxygen balance is of importance in the choiceofplasticizer material. Plasticizers which provide'a substantial part of the oxygen requiremcnt jarc preferred, since. substantially smokeless combustion of the explosive grain composition is highly desirable. ticizers preferably contain high oxygen balance. I prefer to use at least one plasticizer material not containing aromatic nitro groups. The non-nitro group containing plasticizers are preferably selected from the class consist ing of esters ofpolyhydric alcohols and esters of polycarboxylic acids. Combinations of plasticizers such as dinitrotoluene with '2 ,4-dinitrodiphenyl ether and combinations of these with dinitrophenyl propyl ether with or without the addition of the non-nitro group-containmg plasticizer components produce with the solid polyr ial, which when used in the formulation of solid propellants containing ammonium nitrate, results in the production of grains which exhibit excellent resistanceto shattering and deformation when subjected to shock at low orihigh'temperatures. Such grains are found not to be altered with respectto burning properties after being subjected to such shock. Q

The relative amounts of the different plasticizers in the binder material may be varied over a wide range. Thus the plasticizer may consist entirely of 2,4-dinitrodiphenyl etheror may consist entirely of di(dinitrophenyl)-polyglycol e ther, or other nitro compounds such as 2,4-dinitrotoluene may be used with the dinitrodiphenyl others. Likewise, variable amounts of dinitrophenyl propylether- .may be used along with these other nitro compounds.

In general, other known plasticizers for polyvinyl acetate containing no nitro groups, such asthe dialkyl phthalates and; the Flexols, should be used only in conjunction with the nitro compounds as plasticizers for the polyvinyl acctate in the binder material. e

The inorganic combustion catalyst of this invention is selected from the class consisting of ammonium dichromate and Prussian blue.- Certain iron compounds broadly designated as Prussian-blue are effective for the combustion of ammonium nitrate grains containing oxidizable binder materials. These catalysts are the subject matter of U.S patent application filed by Wayne A.'Proell and lwilliam G. Stanley, s 273,564 and-SN. 288,065, filed May 15;, 1952, now abandoned. Mixtures of ammonium dichromate' with insoluble'Prussian' blue may be used.

In general, ammonium dichromate tends to give lower pressure exponents and hence the inorganic catalyst should consist at least partiallyof ammonium dichromate. How- .ever, arr-inorganic catalyst consisting essentially of insoluble Prussian bluemay be, used. 7 ,1. One of the requirements of the solid propellant; composition is chemical stability at relatively high tempera tures." This is related to the gassing tendency as measured ;by the-fl 35 C. gas stability test, which test is described ..based onpolyvinyl acetate binders require an inhibitor hereinbelow; -The ammonium nitrate solid-propellants component in order to reduce gassing of the composi- .tions underrelatively high temperature storage conditions.-- The inhibitors which give satisfactory results are in general alkaline reacting. It has been found that certain amines are particularly effective, for example, 1.3- diaminobenzene, diphenylamine and urea. However, :I

.prefer magnesium oxide as the gassing inhibitorforthese compositions. As indicated hereinabove, these inhib to s. re utilizediu amcuutawit in the range... from Coplasticigers with theijnitroaromatic plasdated to pressure in the formula S about-0.2% to about 3% by weight of the gas-producing composition. 1

Finely divided carbon may be added to the gas-producing compositi'on in amounts up to about 5% by weight, preferably in amounts of 0.5- to 2.0% by weight of the finished grain for the purpose of improving burning rate. Highly adsorptive activated carbons such as ,Norit" and fNuchar make up one class of effective burning rate additives. A second general type of carbon-useful for increasing the burning rate of compositions are the carbon blacks, roughly classified as the channel blacks and the furnace combustion blacks. The carbon blacks are characterized by low ash content, and wby' 'having extremely small particle size, that is, 50 to 5000 A. In order to avoid dusting and afford convenience in handling, some carbon blacks are available bead form. The beads are extremely soft and disintegrate during the mixing of the composition. Examples of bead" type carbon blacks are Micronex beads (channel blacks) and Statex beads (furnace blacks).

A third type of carbon which may be used in the composition is finely ground petroleum coke, particularly petroleum coke obtained as residue in the pipe-stilling of mid-continent heavy residuums. Such coke usually contains less than about 1% ash and hence, like the carbon blacks, is particularly suitable in gas-producing grains Where it is desirable to keep to a minimum solid inorganic particles in the combustion gas. .The coke'may be activated by methods well known in the a'rt to improve the efiiciency thereof as a burning r'ate promoter and it is preferably ground to pass through a #325 U.S. Standard sieve. l Preparation of the compositions of this invention con- 'sist of these three steps: makingthe binder, mixing binder with ammonium nitrate and other ingredients to form a homogeneous solid composition, and molding the finished solid propellant grain. The binder is prepared by adding polyvinyl acetate to a mixture of nitrocompounds and 'plasticizer'at 120-150 C. in a suitable mixer. Mixing is continued until the polyvinyl acetate is completely plasticized. This occurs readily. Blending of the binder with ammonium nitrate and the other components of the formulation may be carried out in the same mixer :if desired. A mixingtemperature of 90 l05 C. afiords a homogeneous somewhat dough-like'solid; If desired,

mixing may be carried out under reduced pressure in order to remove any moisture present in the raw ma- .terials. g i l V Burning rate test strips of the gas-forming composition are prepared by extruding or molding the homo geneous gas-forming composition at a temperature below gen pressure. Four to six'strands are burned at varying pressures between 600 and 1800 p.s.i. Plotting burning rate in inches persecond against pressure on log-log paper gives a straight line. The slope of'this straight line is defined as the exponent of the burning rate as re =where B is the linear burning rate at pressure p,. d is .sthe linearburning rate for the composition at 1000 p.s.i.,

is presure in p.s.i. in the burning chamber and 11" is the pressure exponent showingdependcnce of the burnpositions containing ammonium nitrate, combustion catalyst and binder material by molding under a pressure of about'2000 to 4000 and'shape of the ".tures following the cycle treatment.

grains are dependent upon their intended use. Grains are provided with centrally located holes of different shapes; that is, starform, cruciform or circular. Each: grain has the external surface inhibited by a coating of a material such as asphalt. to restrict burning to the internal surface. Test g'rains subjected to tests described hereinbelow and for usein -a test motor, which grains were 2.75" in diameter and about 4" in length, were provided with a starform centrally located hole. The test data obtained by burning such grains in the test motor indicate overall performance of the compositions when used in assist take-off operations. For these operations the grains are mounted in a conventional case provided with a suitably placed igniter charge such as cannon powder, whiclgris fired electrically. The igniter flame in turn ignites the propellant grain. The temperature of the gases produced by burning of grains may be of the order of 1500 F. to 3400* F. and the pressure or impulse produced by the hot gases will be dependent upon the grain size, diameter of the nozzle, and other factors. The gas-producing grains may be molded into disc-form, stacks of discs being used as gas-forming propellant material for missile rockets.

As indicated hereinabove, the grains of diameter 2.75" inlength are given a thermal shock test which is referred to herein as the cycling test. In this test, grains of a given composition are held in an oven at a temperature of 175 F. for a period of two hours, following which the grains are immediately subjected for a period of two hours to a temperature of F. to complete one cycle. After a second cycle, the grains are permitted to come to room temperature, is, about 75 to F. These grains are examined for indications of cracking,

--crystallinity, and resistance to deformation and shattering when dropped on a concrete surface. Grains are then fired at --75 F., F. and normal ambient tempera- In general, grains made with the plasticized polyvinyl acetate of this invention show no physical defects following the thermal cycling test, and show firing qualities after the cycling .test identical with'grains which have not'been submitted Grains are withdrawn periodically and tested with respect to firing and burning qualities. The best grainslwill not. be affected after 30days or more of high temperature storage. Agrain which will not tolerate prolonged hot storage malperforms ballistically. It may give an erratic dime-pressure curve and may sometimes even burn with explosive violence. In general, the ammonium nitrate grains made up with the plasticized polyvinyl acetate of :this invention are superior with respect to burning per formance after hot aging.

The 135 C. gas stability test which is a measure of the chemical stability and gassing properties of the pro- .pellant com osition is carried out as follows:

connected by tubing to a mercury manometer system which is so arranged that differential'readings of the manometer are translatable into volume changes in the system. Sincethe volume change of the sample itself can be disregarded, the volume change in the system corresponds to the amount of gaseous decomposition prodnets ofthe sample. The Vessel is inserted to an opening in a metal block: this metal block is provided with electi-ic'al heating elements and with controls whichpermit the. blockyto be maintained at a temperaturejof 135 C.

a A period of 15 minutes is allowed for the sample tocorne to the temperature of 135 C. At this time the manometer is zeroed. Readings are taken at 15-minute intervals' 'iintil the gassing rate is substantially cons t an t.

manometer readings are converted to 'cc./g./hr. for each interval. This rate is plotted against the time of heating. In general,;'it is considered that a composition which has a zero'gassing rate during the first hour of heating will be substantially free. of gassing tendency in storage at atmospheric temperatures. The compositions of this invention consisting of defined binder, ammonium nitrate, an inorganic catalyst and an alkaline-reactinginhibitor exhibit extremely low "gassing rates in this tes't." Even the presence'of finely divided carbon does not render the composition unsatisfactory with respect to storage stability at elevated temperatures. I

The following examples are illustrative of -propellant compositions which may be used in the'propelling of rockets and in assist takeofi operationsas described above.

- p Example 1 I -A binder material for an-ammonium nitrate gasforming composition was prepared by mixing at a temperature of about 120 C., 35 partsby weight of polyvinyl acetate with a molten mixture consisting of 45 parts by weight of 2,4-dinitrodiphenyl ether and 20 parts by weight of 2,4- dinitrotoluene. The mixture was stirred to form a homogeneous plasticized mass. This binder material was tough {and rubbery at ambient temperatures. A plasticized am- ,monium nitrate gas-producing propellant composition consisting on aweight'basis of 74% finely ground ammonium nitrate, 23% of the above binder, and 3% insolublePrussian blue catalyst was formulated by mixing to homogeneity at a temperature ofrabout 100" C. A

M? diameter test strand of the finished composition was extruded at a temperature of about 100 C. and a pressure of 2000 p.s.i. This test strip had a burning rate of 0.12 inch per second at 1000 p.s.i. and the pressure ex- .ponent was 0.72.

Example2 I A thermoplastic binder material consisting of 25% by weight of polyvinyl acetate described in Example 1 and 75% by weight of bis(2,4-dinitrophenyl)-triglycol ether .was prepared. This binder was used to formulate a plas- -ti'ciz'ed gas-producing ammonium nitrate composition.

The bis(2,4-dinitrodiphenyl)-triglycol ether was prepared by reacting 2,4-dinitrochlorobenzene with triethylene glycol in mol ratio of 2 to 1 using 50% aqueous sodium hydroxide at a temperature of 105-1 10 C. The binder material was prepared according to the procedure of Example 1. It was rubbery and moderately tough. A gasforming propellant composition was prepared from the above binder by adding at 95 105 C. a mixture of finely ground ammonium nitrate, finely divided carbon in theform of Micronex (Standard) beads, and insoluble Prussian blue, and'mixing the components to homogeneity. The composition consisted of: 1

Component: Percent by weight Ammonium nitrate 76' ,.Bis(2,4-dinitrodiphenyl)triglycol ether 15 'Polyvinyl acetate 5 Prussian blue catalyst 3 .Carbon 1 -'A screw-extruded strand of this composition showed a burning rate of 0.18" per second at 1000 p.s.i. and a pres sure exponent of 0.62. v

Example 3 v A thermoplastic polyvinyl acetate binder was made in a steam-heated mixer according to the method of Example 1 except that triethylene glycol di-Z-ethylhexoate, a com- 'mercial plasticizer known as Flexol 3G0, was substituted forthe dinitrotoluene component. The polyvinyl acetate was Gelva-800. The binder consisted of 40% polyvinyl acetate, 30% 2,4-dinitrodiphenyl ether and 30% Flexol 3G0, and was rubbery and moderately tough. A prophenyl ether (30%), and Flexol SGH (30%). binder was rubbery and tough andwas used in formulating the following gassforming ammonium nitrate compositions according-to the method described in Example 3.

the binder was first softened in the mixer. Finely ground ammonium nitrate admixed with insoluble Prussian blue, 'carbonblack in the form of Micronex beads (Standard), urea and diphenylamine were added and mixed to homogeneityv with thefbinder at a temperature of -105. C. The composition/ofthis propellant composition was:

. A .partof:thispropellant composition was molded in the'form'of 2.75" *sta'r grains at 2000 p.s.i. A 4" length star grain was fired successfully after being subjected successively to temperatures of 75 F. and 175 F. in the thermal cycling test described above. Another 4" star grain was aged for 70 daysat.170 F. during which period it lost about 1% in weight. This aged grain burned smoothly in a rocket motor at a pressure of 1000 psi using a nozzle of 0.20" diameter.

Another binder consisting of 40% polyvinyl acetate, 40% Flexol 3G0 and 20% 2,4-dinitrodiphenyl ether was prepared. A gas-producing propellant composition was formulated according to the procedure outlined in Example 1 by mixing with the binder material finely divided ammonium nitrate containing admixed therewith equal amounts of diphenylamine and urea stabilizenfinely di- 'vided, carbon in the form of Micronex beads and a small amount of surfactant, that is, 0.1% (based on the weight of the formulation) of the commercial product Span '85which is sorbitan trioleate. The gas-forming compo;

sition consisted of 79.9% ammonium nitrate, 5.6% polyvinylacetate 5.6% 'Flexol3GO, 2.8% 2 ,4' dinitrodiaphenyl ether, 1.5% insoluble Prussian blue catalyst, 1.5%

lowing this test. After 36 daysof hot storage ,F.)

these grains showed weight loss of less than 0.2%'.. The burning rateof test strands was 0.11 inches per second at .1000 p.s.i. and the pressure exponent was'0.60.

' Example 4 r j -A thermoplastic polyvinyl acetate binder was prepared in a steam-heated mixer according to the method of Example 3 from polyvinyl acetate 1 (40%), 2,4-dinitrodi- The . 4a Component: Wt. percent Polyvinyl acetate. 4.8 DNDPE v 3.6 Flexol 3GH- 3.6 Prussian blue 3.0 Carbon black 1.0 NH NO 84.0

4b Component: Y Wt. percent Polyvinyl acetate 14.8 'DNDPE" 3.6 Flexol.3 ,GH 3.6 ""Prussian blue- --3.'0 Carbon black? j v I 1.' O Magnesium oxide 1.0 NH NO 83.0

' Gelva-BOOJ 1 '='2,4-dlnitrodlphen1ether. "Micronex beads( tandard).'

asses-a Component: V I Wt perc'ent P01yvinyl' acetate 4.8 DNDPE. I 3.6 Flexol 36H ....i, 3.6' :Ammonium dichromate 3.0 vCarbon blaclc L 1.0 Ammonium nitrate 84.0

Component: 1 Wt. percent Polyvinyl acetate as. "-4.-. t 4.8 DNDPE 1 a -l- 3.6. Flexol 3GH 3.6- Ammonium dichromate 3.0 Carbon black 2 1.0

Magnesium oxide 1.0 Ammonium nitrate ..c 83.0

4e Component: Wt. percent Polyvinyl acetate 4.8 DNDPE 1 3,6 Flexol 3GH 3.6 Ammonium diehromate 1.0 Prussian blue 2.0 Carbon black 1.0 Magnesium oxide 1.0 Ammonium nitrate 83.0 1 2,4-dinitrodlphenyl ether. Mlcronex beads (Standard). I

Formulation 4a showed excessive, gassing after 15 minutes at 135 C. Formulation 4b showed no gassing during 7 hours after which the gassing rate was extremely low. f

Test strands of the above compositions were molded at 2000 p.s.i. and burned in the Crawford bomb. The results are tabulated below:

Pressure Burning Rate, Formulation Inches/Sec. at Exponent 1,000 p.s.i.

Example A binder material was prepared according to the procedure described in Example 1 by adding polyvinyl acetate (40%) i.e., Gelva-800, mixture of dioctyl phthalate (30%), 2,4-dinitrodiphenyl ether (10%) and bis(2,4-dinitrophenyl)polyglycol 200 ether The bis(2,4- dinitrophenyl) polyglycol 200 ether was prepared according to the following procedure: A mixture of 1275 grams (6.3 mols) of a commercial grade 2,4-dinitrochlorobenzene and 629 grams (3.1 mols based on a molecular weight of 200) of polyethylene glycol 200 was stirred to obtain an intimate mixture. To this mixture was added dropwise 284 grams of sodium hydroxide dissolved in 300 milliliters of water over a period of 45 minutes. The temperature of the reaction mixture was maintained between 105 -1 12 C. and was stirred for an additional one and one half hours following which the reaction mixture was added to about 3800 milliliters of water with stirring. The washed oil product was separated from the wash water and the washing procedure was repeated five times, the last wash water being made slightly acid with dilute hydrochloric acid. The product was dissolved in benzene and the residual water was removed by distillation with 10 the benezenein vacuo at 100 C. and 2mm. ressure-.- The ash content of the product was 0.12%. Th'e'nitrogen content was 10.51%." Calculated nitrogen contentpwas 10.61%. f

The binder material prepared with the polyvinyl acetate plasticize'd with dioctyl: 'phthal'ate, '2,4-dinit'rodiplrenyl ether, and bis(2,4dinitrophenyl )polyglycol '2'001etl1er was rubbery and moderately tough. '1

"In preparing the ammonium nitrate gas forrning com position, 85.4 parts by weight of finely divided ammonium" nitrate was intimately mixed with 1.5 parts by weight of insoluble Prussian blue catalyst,"1.5 parts by weight of ammonium dichronrate, '1 part by weight of finely dividedcarbon in the formof Micronex beads, 0.75 parts by weight of di henylamine and 075 parts by Weight of urea. These was also added to the ammonium nitrate 0.1 part by weight of Arlacel C surfactant i.e., sorbitari' sesquioleate, and the mixture of ammonium nitrate, binder and other components was stirred to homogeneity at I bis(2,4-dinitrophenyl)polyglycol 200 ether 1.8%, Prus sr'an blue 1.5%, ammonium dichromate 1.5 carbon 1%, diphenylamine 0.75%, urea 0.75%, surfactant 0.1%, and ammonium nitrate 85.4%. A part of this compo sition was molded into burning" strands. Cylindrical propellant grains having a'diameter of 2.75 and provided with a star-shaped internal aperture, were molded, at about 2000 pounds per square inch pressure." Some. of these grains were cycled in the thermal cycling test and were fired successfully in the test motor following =the cycling test. Another of these grains was fired successfully after being subjected'to a storage temperature of F. for a period of 13 days. The motor burning rate was about 0.18 inch per second at 1000 p.s.i.

Example 6 A binder material consisting of polyvinyl acetate (40%), 2,4-dinitrodiphenyl ether 10%), triethylene glycol di-2-ethylbutyrate (20%), (Flexol 3GH) and 2,4- dinitrophenyl propyl ether (30%) was prepared according to the method described in Example 1. The binder was moderately tough and rubbery. The 2,4-dinitrodiphenyl ether and the 2,4-dinitrophenyl propyl ether were prepared according to the method described in the above application S.N. 465,132, normal propyl alcohol being substituted for the phenol in the preparation of the 2,4 dinitrophenyl propyl ether. This binder was used in preparing a solid propellant mixture in the manner described in Example 5.

The finished composition contained on a weight basis, the following:

Component: Wt. percent .Ammonium nitrate 81.0 Binder 14.0 Ammonium dichromate 2.0 Prussian blue 1.0 Micronex beads (Standard) 1.25 Magnesium oxide 0.75

The finished composition was molded into cylindrical grains having-a diameter of 2.75". Nine motor firings were made on cycled grains. Three at 75 F., three at ambient temperatures and three at F. The grains showed uniformly satisfactory firing behavior in the test motor using a 0.222"30 nozzle. The grains were particularly resistant to physical shock. One of the cycled grains was dropped from a height of eight feet onto concrete and then was fired successfully in the test motor. The grains were also subjected to hot storage at 170 F. and fired satisfactorily following 30 days storage at this temperature. Burning tests made with molded s erts 12 strandsindicated aburning rate of 0.15 pei secondat about 0.2 and 3 weight percent 'of an alkaline gassing l 00 'p.s.i. and aprjes'sureexponent of 0.47. inhibitor from the class consisting of diaminobenzene, Percentage compositions in this specification and claims diphenylamine, urea and magnesium oxide. based thereon are percentages by weight unless india '2. The composition'as described in claimjflgwherein cated otherwise. v i the? inorganic catalyst consists of'a mixture of insoluble Having thus described' my, invention, I claim: Prussian blue and ammonium -dichr'ornate-.-- 1'. vA gas-forming composition consisting essentially of 3. The composition as described-iniclaim' l whcrein (a) between about 70"and about90 weight percent of the inorganic catalyst consists-essentially of insoluble ammoniumnitrate, (b) betweenabout 1 and 5 Weight Prussian blue. percent of an inorganic combustion catalyst selected from 10. 4. The composition of claim 1 to which is added from the class consisting .of ammonium dichromate and Prusabout .5 toabout 2% of finely divided carbon, 1 sian blue, (c) betwe'en"about' 5 an'd'25 weight percent 5. The composition as described in claimlto which of plastic binder material, said material consisting of (i) is added from about 0.2 to about 3% by "weight, of mag. between about 20 and 60 weight percent of polyvinyl nesium oxide. 1 acetate and (ii) .a plasticizer selected from the class 6. A shaped gas-forming grain consisting essentially i l consisting of (l) nitro-substituted'aromatic, compounds on a weight basis, of. ammonium nitrate, about 81%, l l

corresponding to the formula l I insoluble Prussian blue about 1%, about 2%. 0t ammonium dichromate, about 5.6%.. polyvinyl acetate of viscosity of 700 to 900 centipoises at C., 2,4-dinitrodi- :3 R I I v I 20 phenyl ether about 1.4%, 2,4-dinitrophenyl propyl ether I about 4.2% and triethylene glycol di-2-ethylbutyrate about where R isi selected frorn the class consisting of nitroofmagmsium Oxide-l phenyl, phenoxy, mononitrophenoxy and alltoxy contain- 2.8%, about 1.25% of carbonblack and abo'ut 0.75% a J References'Cited 'i'n'the'file of this patent ing from 1 to 4 carbonv atoms, (11 nitrophenyl glycol I v ether wherein said glycol-portion affording compound UNITED STATES PATENTS I has a molecularweight of not more than aboutZOO and 2,159,234 I Taylor May 23, 1939 (III) mixtulesofsaid nitro-substitutedaromatic com- 1 pou'ndsselected-from vI and, H with amember selected FOREIGN TE S l a from the class; consisting, of dialkyl phthalates, triethyl 55,535 Great Britain. J 5 95 citrate, tributyl-citrat'e,,diethyl tartrate, dibutyl tartrate, I l triglycol dialkanoat es, polyglycol. dioctanoate,dial kyl di; ER 1 I l Y glycolates, dinitrobenzene tanddinitrotoluene, said mix- Bebie: Manual of Explosives, Military Pyrotechnics ture containingat least about 30 weight percent of'said and Chemical Warfare Agents, The MacMillan C0,,

intro-substituted aromatic compounds and (d)v between New York (1943), pages 57, 58, 60, 61, 62. 

1. A GAS-FORMING COMPOSITION CONSISTING ESSENTIALLY OF (A) BETWEEN ABOUT 70 AND ABOUT 90 WEIGHT PERCENT OF AMMONIUM NITRATE, (B) BETWEEN ABOUT 1 AND 5 WEIGHT PERCENT OF AN INORGANIC COMBUSTION CATALYST SELECTED FROM THE CLASS CONSISTING OF AMMONIUM DICHROMATE AND PRUSSIAN BLUE, (C) BETWEEN ABOUT 5 AND 25 WEIGHT PERCENT OF PLASTIC BINDER MATERIAL, SAID MATERIAL CONSISTING OF (I) BETWEEN ABOUT 20 AND 60 WEIGHT PERCENT OF POLYVINYL ACETATE AND (II) A PLASTICIZER SELECTED FROM THE CLASS CONSISTING OF (I) NITRO-SUBSTITUTED AROMATIC COMPOUNDS CORRESPONDING TO THE FORMULA 